Antenna unit and portable radio system comprising antenna unit

ABSTRACT

A subject of the present invention is to provide an antenna unit and a portable radio device capable of attaining a wider bandwidth and a lower SAR.  
     In the present invention, an antenna element ( 12 ) that has an effective length corresponding to a half wavelength of a transmitting frequency and a parasitic element ( 13 ) that has an effective length corresponding to a half wavelength of a receiving frequency are provided, an antenna current is induced in the antenna element ( 12 ) at the transmitting frequency upon transmitting a radio wave in a predetermined transmitting frequency band, and another antenna current is induced in the parasitic element ( 13 ) by a spatial coupling between the antenna element ( 12 ) and the parasitic element ( 13 ) at the receiving frequency upon receiving the radio wave in a predetermined receiving frequency band, whereby peak points in an antenna current distribution are scattered into two points. Accordingly, a wider bandwidth can be obtained without addition of a matching circuit and also expansion of a parts packaging space on a board and reduction in the number of packaged parts can be achieved.

TECHNICAL FIELD

The present invention relates to an antenna unit used in a portableradio device and a portable radio device equipped with this antennaunit.

BACKGROUND ART

The mobile radio communication system recently spreads. In the portableradio device, or the like, for example, the user anticipates furtherreduction in size, weight and cost of the device. Also, the portableradio device capable of meeting a plurality of communication systemsthat make transmission/reception in a plurality of different frequencybands is now investigated. Thus, the user expects the device to handlethe frequency bands of a plurality of communication systems by oneantenna unit. As a result, a smaller size, a lower cost attained by thereduction in the number of articles and the assembling man-hours, or awider frequency characteristic to be secured, and so forth are requiredof the antenna unit that is incorporated into the portable radio device.However, normally the antenna unit tends to have a narrower bandwidthcommonly when the size of such antenna unit is reduced smaller.

Meanwhile, as the antenna unit used in the portable radio device in theprior art, e.g., the mobile phone, the antenna unit shown in FIG. 1 isknown. In this case, FIG. 1 is an appearance view of the antenna unitshowing the state that a whip antenna 202 is pulled out from aconventional mobile phone 200.

This mobile phone 200 has a telescopic antenna unit. The whip antenna202 starts operation when such whip antenna 202 is pulled out from ahousing 201. Also, a helical antenna 203 starts operation when the whipantenna 202 is pushed into the housing 201.

By the way, according to this telescopic antenna unit, the helicalantenna 203 of this antenna unit is always protruded from the housing201 of the mobile phone 200 to the outside, and thus the presence ofsuch protruded portion causes inconvenience to the user upon carryingand operating the phone. In particular, the small-size mobile phone 200is often put into the user's breast pocket. For this reason, it ispossible that, since the antenna when protruded as it is may hit onvarious things during conveyance of the phone, a physical strength ofthe antenna cannot be satisfactorily kept.

Therefore, in order to overcome disadvantages such as such troublesome,such incomplete physical strength, and the like, the built-in antennaunit whose antenna element is built in the interior of the main body ofthe portable radio device is known, as disclosed in JP-A-2000-349526,for example.

However, since this built-in antenna unit is arranged in vicinity of theliquid crystal screen, the board, the speaker, etc. constituting theportable radio device, such antenna unit is easily affected by theseparts. It is known that normally such antenna unit operates in thenarrower bandwidth.

For this reason, in many cases the wider bandwidth is realized byproviding the matching circuit to the preceding stage of the feedingportion and then adjusting the impedance matching.

However, in the case where the wider bandwidth is realized by thematching circuit, a space in which the matching circuit is mounted mustbe kept on the printed board in the housing. Thus, there is apossibility that an increase in the mounting space on the printed boardand an increase in the number of articles are brought about.

Also, normally the telescopic antenna unit in the prior art isconstructed such that such device is unbalancedly fed to flow theantenna current through the housing of the portable radio device. Insuch unbalanced antenna unit, it is known that the antenna gain isdegraded by the influence of the user's hand, and so on when the userholds the portable radio device to use.

Also, this portable radio device is regulated by the law based on SAR(Specific Absorption Rate), and it is requested to suppress the SARvalue below a predetermined value. In such portable radio device,normally the state in which the user puts the portable radio device tohis or her ear to contact closely to the head of the human body andspeaks upon the phone, and so forth, for example, are considered as “thestate in which the SAR value is increased”. Thus, according to theregulation by the law, further reduction in the SAR value is driven bynecessity.

Therefore, as approaches of reducing the SAR value during the speakingin the prior art, three approaches described in the following areconsidered, for example.

{circle around (1)} First, it is known that the SAR value can be reducedby increasing an air clearance between the antenna unit and the head ofthe human body. Since normally the earpiece portion comes closest to theear during the speaking, mainly a distance between the earpiece portionand the ear should be extended herein. However, in order to increasethis air clearance, the antenna element must be positioned away from thehead of the human body during the speaking by enlarging the housing ofthe portable radio device, for example. Thus, there is a possibility ofcausing an increase of the device in size.

{circle around (2)} Second, it is known that the SAR value can bereduced by reducing a set value of the maximum sending power. However,there is a possibility that the communication quality in the weakelectric field area cannot be kept when the set value is reduced.*

{circle around (3)} Third, as disclosed in JP-A-11-307144, the SAR valuecan be reduced by increasing an air clearance between a peak point ofthe antenna current (a point at which the largest antenna current isgenerated) and the head of the human body. This approach is available inthe configuration in which the peak point is separated away from thehead of the human body during the speaking. However, in the antenna unithaving the configuration set forth in this publication, the peak pointof the antenna current is only one and thus the peak point comes closeto the head of the human body according to a mode of use of the user.Thus, there is a possibility of increasing the SAR value.

Here, the SAR value as the object of the law regulation is the numericalvalue used when the radio wave is radiated from the antenna unitprovided to the portable radio device. Since there is no need to takeaccount of such value upon receiving the radio wave, only thetransmission band should be checked.

Next, FIG. 2 is an explanatory view showing the radiation directivitywhen a parasitic element 213 is brought close to an antenna element 212.

In FIG. 2, the antenna element 212 is a monopole antenna whose effectivelength is a half wavelength (λ/2) of a transmitted wavelength (λ), andis fed from a feeding portion 214. In contrast, the parasitic element213 is formed of a wire, or the like, for example, whose length isshorter than the half wavelength (λ/2), and is arranged in the proximityof the antenna element 212.

In the case of an antenna unit 210 having such configuration, it isknown that the parasitic element 213 operates as a waveguide element andthus the radiation directivity of the antenna unit 210 becomes strong inthe +X direction rather than the −X direction.

-   (1) As explained above, normally the bandwidth of the above    conventional antenna unit is liable to become narrower when the    reduction of the antenna unit in size is advanced.-   (2) Also, in the case of the above conventional telescopic antenna    unit, there are the problems that the protrusion of the antenna unit    from the portable radio device causes inconvenience upon carrying    and operating the phone, and in addition the physical strength    cannot be kept.-   (3) Also, since the above conventional built-in antenna unit    disclosed in above JP-A-2000-349526 is arranged in vicinity of the    liquid crystal screen, the board, the speaker, etc. constituting the    portable radio device, normally the bandwidth tends to become    narrow.-   (4) Also, in the above conventional unbalanced antenna unit, there    is the problem that the antenna gain is degraded by the influence of    the user's hand when the user holds the portable radio device to    use.-   (5) Also, in the above conventional portable radio device, the    increase in size of the device is brought about when the air    clearance between the antenna unit and the head of the human body is    increased during the speaking state to reduce the SAR value.-   (6) Also, in the above conventional portable radio device, there is    the disadvantage that the communication quality is degraded in the    weak electric field area when the set value of the maximum sending    power is decreased to reduce the SAR value.

Here, current distributions 222 to 252 and current peak points 221 to251 in respective antennas of a half-wave monopole antenna 220, aone-wave monopole antenna 230, a half-wave dipole antenna 240, and aone-wave dipole antenna 250 will be explained with reference to FIGS.3(A) to (D) hereunder.

As shown in these Figures, it is appreciated in these monopole antennasand dipole antennas that, in the case of the half wavelength, thecurrent peak points 221 to 251 are positioned in one center point of theantenna element respectively and, in the case of the one wavelength, thecurrent peak points are scattered into two points respectively.

On the contrary, in the antenna unit set forth in above JP-A-11-307144,there are the problems that the peak point of the antenna current isonly at one location, and the peak point comes close to the head of thehuman body according to change in the using situation of the user, andthus the SAR value is apt to increase.

Therefore, the present invention has been made in light of abovecircumstances, and it is an object of the present invention to providean antenna unit and a portable radio device capable of realizing a widerband and realizing a good antenna performance by controlling theradiation directivity and in addition reducing SAR.

DISCLOSURE OF THE INVENTION

First, an antenna unit of the present invention provides an antenna unitused in a portable radio device, said antenna unit comprising an antennaelement and a parasitic element, wherein the antenna element has aneffective length corresponding to a half wavelength or one wavelength ofa transmitting frequency, to induce an antenna current that radiates thetransmitting frequency upon transmitting a radio wave in a predeterminedtransmitting frequency band, and wherein the parasitic element has aneffective length corresponding to a half wavelength of a receivingfrequency, to induce another antenna current by a spatial coupling withthe antenna element upon receiving the radio wave in a predeterminedreceiving frequency band.

According to this configuration, the antenna current is induced in theantenna element at the transmitting frequency, while another antennacurrent is induced in the parasitic element at the receiving frequencyby the spatial coupling between the antenna element and the parasiticelement. Therefore, a wider bandwidth can be obtained without provisionof a matching circuit and also expansion of a parts packaging space on aboard and reduction in the number of packaged parts can be achieved.

Also, in the radio communication system in which a frequency in thetransmitting band is lower than a frequency in the receiving band, theradiation directivity can be easily directed to the outside of theportable radio device and thus the good antenna performance can beobtained.

Also, in the case of the antenna element whose effective lengthcorresponds to one wavelength, the radio wave is emitted mainly from theantenna element at the time of transmission whereas the radio wave isemitted slightly by the coupling from the parasitic element whoseeffective length corresponds to one wavelength. Therefore, the peakpoint of the antenna current can be scattered into three points intotal, i.e., two peak points of the current in the one-wave element andone peak point of the current in the half-wave element, and thus the SARvalue can be reduced.

Similarly, in the case of the antenna element whose effective lengthcorresponds to one wavelength, in the radio communication system inwhich the frequency in the transmitting band is set lower than thefrequency in the receiving band, the radiation directivity can be easilydirected to the outside of the portable radio device and thus the goodantenna performance can be obtained.

Second, an antenna unit of the present invention provides an antennaunit used in a portable radio device, said antenna unit comprising anantenna element and a parasitic element, wherein the antenna element hasan effective length corresponding to a half wavelength of a receivingfrequency, to induce an antenna current upon receiving a radio wave in apredetermined receiving frequency band, and wherein the parasiticelement has an effective length corresponding to a half wavelength of atransmitting frequency, to induce another antenna current by a spatialcoupling with the antenna element upon transmitting the radio wave in apredetermined transmitting frequency band.

Accordingly, in this configuration, the antenna current is induced inthe antenna element at the receiving frequency, while another antennacurrent is induced in the parasitic element at the transmittingfrequency by the spatial coupling between the antenna element and theparasitic element. Therefore, the wider bandwidth can be obtainedwithout provision of the matching circuit and also expansion of theparts packaging space on the board and reduction in the number ofpackaged parts can be achieved.

Also, similarly to the first invention, in the radio communicationsystem in which the frequency in the transmitting band is set higherthan the frequency in the receiving band, the radiation directivity canbe easily directed to the outside of the portable radio device and thusthe good antenna performance can be obtained.

Third, an antenna unit of the present invention provides an antenna unitused in a portable radio device that executes transmission/receptionbased on a communication system using radio waves in a plurality ofdifferent wavelength bands, said antenna unit comprising an antennaelement and a parasitic element, wherein the antenna element has aneffective length corresponding to a half wavelength or one wavelength ofa frequency in one communication system, to induce an antenna currentupon using one communication system, and where the parasitic element hasan effective length corresponding to a half wavelength of a frequency inother communication system, to induce another antenna current in theparasitic element by a spatial coupling with the antenna element uponusing the other communication system.

According to this configuration, the antenna current is induced in theantenna element during the operation of one communication system, whileanother antenna current is induced in the parasitic element by thespatial coupling between the antenna element and the parasitic elementduring the operation of the other communication system. Therefore, thewider bandwidth can be obtained without provision of the matchingcircuit and also expansion of the parts packaging space on the board andreduction in the number of packaged parts can be achieved.

Also, the radio wave is radiated from the half-wave or one-wave antennaelement and the half-wave parasitic element, both being coupledelectrically with each other. Therefore, the peak point of the antennacurrent can be scattered into three points and thus the SAR value can bereduced.

Fourth, in the antenna unit of the present invention, in the antennaunit that is employed in the portable radio device, in the portableradio device of the first or third invention, the portable radio devicefurther comprises an earpiece portion, and a distance between theearpiece portion and the antenna element is set larger than a distancebetween the earpiece portion and the parasitic element.

According to this configuration, the earpiece portion such as a speaker,or the like for transmitting the speaking contents to the user isprovided. Since the antenna current is induced mainly in the antennaelement at the time of transmission, the air clearance between theuser's ear and the peak point of the antenna current is enlarged andthus the SAR value can be reduced.

In contrast, the antenna current is induced mainly in the parasiticelement at the time of reception, and thus the air clearance between theuser's ear and the peak point of the antenna current becomes smallerthan that at the time of transmission. But the SAR value is thenumerical value that is required only of the transmission, and thereforeno problem arises at the time of reception.

Fifth, in the antenna unit of the present invention, in the antenna unitthat is employed in the portable radio device, in the second invention,the portable radio device further comprises an earpiece portion, and adistance between the earpiece portion and the antenna element is setshorter than a distance between the earpiece portion and the parasiticelement.

According to this configuration, since the antenna current is inducedmainly in the parasitic element at the time of transmission, the airclearance between the user's ear and the peak point of the antennacurrent is enlarged and thus the SAR value can be reduced.

In contrast, the antenna current is induced mainly in the antennaelement at the time of reception, and thus the air clearance between theuser's ear and the peak point of the antenna current becomes smallerthan that at the time of transmission. But the SAR value is thenumerical value that is required only of the transmission, and thereforeno problem arises at the time of reception.

Sixth, in the antenna unit of the present invention, in the antenna unitaccording to any one of the first to fifth inventions, the antennaelement and the parasitic element are formed by printed patterns on asheet of printed board.

According to this configuration, the antenna element and the parasiticelement can be formed on a sheet of printed board, and thus the numberof articles can be reduced.

As a result, the air clearance between the antenna element and theparasitic element can be fixed with high precision and also suchconfiguration is excellent in the mass-producibility.

Seventh, in the antenna unit of the present invention, in the antennaunit according to the sixth invention, electronic parts are packaged onthe printed board.

According to this configuration, the matching circuit of the antennaunit, which is originally mounted on the main board on which the ICssuch as the radio portion, the logic portion, etc. are to be mounted,can be packaged on another board. Thus, a packaging space on the mainboard can be extended.

Eighth, in the antenna unit of the present invention, in the antennaunit according to any one of the first to fifth inventions, the portableradio device further comprises a radio portion and a printed board onwhich the radio portion is mounted, and the antenna element and theparasitic element are formed by printed patterns on the printed board.

According to this configuration, the antenna element and the parasiticelement can be formed on the main board, and thus the number of articlescan be reduced.

Ninth, in the antenna unit of the present invention, in the antenna unitaccording to any one of the first to eighth inventions, any one or bothof the antenna element and the parasitic element is or are shaped like ameander shape.

According to this configuration, any one or both of the antenna elementand the parasitic element may be shaped in small size.

Tenth, in the antenna unit of the present invention, in the antenna unitaccording to any one of the first to ninth inventions, the antennaelement is balancedly fed.

According to this configuration, degradation of the antenna gain of theantenna unit caused by the influence of the user's hand can be reducedin the frequency band in which the antenna current is induced mainly inthe antenna element to communicate

Eleventh, in the antenna unit of the present invention, the antennaelement and the parasitic element are arranged in an interior of ahousing of the portable radio device.

According to this configuration, since the antenna is never exposed tothe outside of the housing, the antenna unit and the portable radiodevice, which are by no means damaged by the contact, have a highreliability, and are convenient to use, can be realized.

Also, a portable radio device of the present invention having theantenna unit set forth in any one of the first to tenth inventions.

According to this configuration, since any one of above antenna units isprovided, the portable radio device having the same advantages as thoseachieved by the antenna units can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a mobile phone in the priorart;

FIG. 2 is an explanatory view showing the radiation directivity when aparasitic element is brought close to a conventional antenna element;

FIGS. 3(A) to (D) are views showing a current distribution in theconventional monopole antenna and a peak point of the currentrespectively, wherein (A) and (C) show the conventional monopole antennaand (B) and (D) show the conventional dipole antenna;

FIG. 4 is a schematic perspective view showing a mobile phone into whichan antenna unit according to a first embodiment is incorporated;

FIG. 5 is a schematic perspective view showing a mobile phone into whichan antenna unit according to a second embodiment is incorporated;

FIG. 6 is a schematic perspective view showing a mobile phone into whichan antenna unit according to a third embodiment is incorporated;

FIG. 7 is a schematic perspective view showing a mobile phone into whichan antenna unit according to a fourth embodiment is incorporated;

FIG. 8 is a schematic perspective view showing a mobile phone into whichan antenna unit according to a fifth embodiment is incorporated;

FIG. 9 is a sectional view showing the mobile phone according to thefifth embodiment and taken along a IX-IX line in FIG. 8;

FIG. 10 is a schematic perspective view showing a mobile phone intowhich an antenna unit according to a sixth embodiment is incorporated;

FIG. 11 is a sectional view showing the mobile phone according to thesixth embodiment and taken along a XI-XI line in FIG. 10;

FIG. 12(A) is a perspective view showing an antenna unit according to aseventh embodiment, (B) is a schematic perspective view showing a mobilephone into which this antenna unit is incorporated, and (C) is asectional view taken along a XII-XII line in (B);

FIG. 13(A) is a perspective view showing an antenna unit according to aneighth embodiment, (B) is a schematic perspective view showing a mobilephone into which this antenna unit is incorporated, and (C) is asectional view taken along a XIII-XIII line in (B);

FIG. 14 is a schematic perspective view showing a foldable mobile phoneinto which the antenna unit according to the eighth embodiment isincorporated;

FIG. 15 is a partially-broken perspective view showing a mobile phoneinto which an antenna unit according to a ninth embodiment isincorporated;

FIG. 16 is a schematic perspective view showing a back surface of amobile phone into which an antenna unit according to a tenth embodimentis incorporated; and

FIG. 17 is a schematic perspective view showing a mobile phone intowhich an antenna unit according to an eleventh embodiment isincorporated.

In above Figures, a reference numeral 10 refers to a mobile phone, 11(rod-like) to a housing, 11A to an upper housing, 11B to a lowerhousing, 12 to an antenna element, 13 to a parasitic element, 14 to afeeding portion, 20 to a mobile phone, 22 to an antenna element, 23 to aparasitic element, 30 to a mobile phone, 32 to an antenna element, 33 toa parasitic element, 40 to a mobile phone, 42 to an antenna element, 43to a parasitic element, 50 to a mobile phone, 52 to an earpiece portion,52A to a listening point, 60 to a mobile phone, 62 to an earpieceportion, 62A to a listening point, 70 to a mobile phone, 71 to a mainboard, 72 to a printed board, 74 to a feeding pin, 80 to a mobile phone,82 to a printed board, 83 to a main board, 84 to a packaged parts, 85 toa connector connection terminal, 86 to a coaxial cable, 87 to a radioportion, 90 to a mobile phone, 91 to a liquid crystal display portion(LCD), 92 to a printed board, 93 to a radio portion, 94 to a coaxialcable, 100 to a mobile phone, 102 to a printed board, 104 to a feedingportion, 110 to a mobile phone, 120 to a mobile phone, and α, β, γ to anelectrode (pole).

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be explained in detail withreference to the accompanying drawings hereinafter.

First Embodiment

FIG. 4 is an appearance view of the back surface side of a mobile phone10 of a W-CDMA (Wideband Code Division Multiple Access) system intowhich an antenna unit according to a first embodiment of the presentinvention is incorporated. FIG. 4 shows a perspective view when anot-shown LCD (Liquid Crystal Display) screen and a key portion arearranged to direct toward the back of this sheet. In this case, as withthe transmitted/received frequencies in this W-CDMA system, thetransmitting frequency is set to 1920 MHz to 1980 MHz and the receivingfrequency is set to 2110 MHz to 2170 MHz.

The mobile phone 10 shown in FIG. 4 has an antenna element 12 and aparasitic element 13 in a rod-like housing 11. For example, a size ofthis housing 11 has a length of 110 mm in the longitudinal direction, alength of 40 mm in the width direction, and a length of 15 mm in thethickness direction. The LCD and the key portion, although not shown,are arranged on an upper portion and a lower portion of a surface of thehousing 11.

The antenna element 12 is composed of a half-wave dipole antenna that isfed from a feeding portion 14 in the antenna center, and an effectivelength corresponds to a half wavelength (v/fe×½, v: light velocity) ofthe transmitting frequency (fe). In the case of the present embodiment,this antenna element is formed of an about 77 mm copper wire.

Meanwhile, in order to make it possible for the radio wave to arrive atthe antenna element 12 effectively without generation of the standingwave in the case where no parasitic element 13 is arranged, it ispreferable that a VSWR (Voltage Standing Wave Ratio) value should besuppressed lower than 2.5. Therefore, in the case of the presentembodiment, the transmitting frequency band is set to almost 1910 to1990 MHz in the antenna element 12. Thus, the bandwidth is set to almost80 MHz.

The parasitic element 13 is pasted onto an upper end surface of theinterior of the housing 11, for example, and an effective lengthcorresponds to a half wavelength (v/fr×½, v: light velocity) of thereceiving frequency (fr). In the case of the present embodiment, thisparasitic element is formed of an about 70 mm copper wire. Also, theparasitic element 13 is arranged in the proximity of the antenna element12 at an air clearance d of about 10 mm.

Also, the receiving frequency of the parasitic element 13 is set to 2100to 2170 MHz because the VSWR value is set to about 2.5 or less.

Next, an operation of the antenna unit in the present embodiment will beexplained hereunder.

The radiation of the radio wave is executed from both the balancedantenna element 12 excited by the feeding portion 14 and the parasiticelement 13 that is coupled electrically with the antenna element 12. Theantenna element 12 mainly operates as a radiator in a transmitting band,and also the parasitic element 13 operates as a receiver in a receivingband. Therefore, the frequency band of this antenna unit in which theVSWR is 2.5 or less exists in about 1910 to 1990 MHz and about 2100 to2179 MHz, and also a sum of bandwidths becomes about 150 MHz. Theincorporation of the parasitic element 13 yields the wider bandwidth.

Also, in the antenna unit in the present embodiment, the electricalcoupling strength is changed in dependence on the air clearance dbetween the antenna element 12 and the parasitic element 13. As aresult, in the case where the effective length of the antenna element 12correspond to a half wavelength of the transmitting frequency in thesituation that no parasitic element 13 is incorporated, sometimes theresonance frequency in the transmitting band is changed after theparasitic element 13 is incorporated into the device.

In such case, the resonance frequency must be mated with thetransmitting frequency by finely adjusting an element length of theantenna element 12 while the parasitic element 13 is incorporated.Consequently, the effective length of the antenna element 12 after theparasitic element 13 is incorporated is given as a length obtained whenthe resonance is generated at the frequency fe of 1920 to 1980 MHz.

For instance, suppose in this embodiment that the wavelength of theradio wave when the transmission is carried out at the transmittingfrequency (fe) is (λe) and also the effective length of the antennaelement 12 corresponds to the half wavelength (λe/2), the element length(L) is given by $\begin{matrix}\begin{matrix}{L = {\lambda\quad{e/2}}} \\{= {v/( {2{fe}} )}}\end{matrix} & (1)\end{matrix}$where v: propagation velocity of the radio wave (light) Hence, theelement length of the antenna element 12 is derived as 75.7 mm to 78.1mm from Equation (1).

Similarly, the effective length of the parasitic element 13 must also befinely adjusted, and is derived as a length that resonates at thereceiving frequency fr of 2110 to 2170 MHz when incorporated.

For instance, suppose that the half wavelength (λr/2) of the wavelength(λr) of the radio wave at this receiving frequency (fr) corresponds tothe effective length of the parasitic element 13, the element length (L)of the parasitic element 13 is derived as 69.1 mm to 71.0 mm.

In this case, the effective length of the antenna element 12 must beadjusted within a range of ±10% after the parasitic element 13 isincorporated since such antenna element is also coupled weakly with theparasitic element 13 at the transmitting frequency. Therefore, in thisembodiment, the length of the antenna element is set to almost 77 mm asdescribed above.

Similarly, the effective length of the parasitic element 13 must beadjusted within a range of ±10% after this parasitic element 13 isincorporated. Therefore, in this embodiment, the length of the parasiticelement 13 is set to almost 70 mm as described above.

Also, the radiation directivity of the present antenna unit results inthe strong radiation in the +X1 direction rather than the −X1 directionsince the parasitic element 13 acts as the waveguide element. Since thetransmitting frequency is lower than the receiving frequency in theW-CDMA system, the above radiation directivity can be obtained bypasting the parasitic element 13 whose element length is shorter thanthe antenna element 12 onto the upper end surface of the interior of thehousing 11.

Also, the degradation of the antenna gain is easily brought about by theinfluence of the not-shown board and electronic parts in the housing 11if the radiation in the (−X1) direction of the inside of the housing 11is enhanced conversely to the configuration in this embodiment. But thegood antenna performance can also be obtained by enhancing the radiationin the outward direction as in this embodiment.

In this manner, according to the present embodiment, the antenna currentis induced in the antenna element 12 at the transmitting frequency,while the antenna current is induced in the parasitic element 13 at thereceiving frequency by the spatial coupling between the antenna element12 and the parasitic element 13. Therefore, the bandwidth can beexpanded without addition of the matching circuit, and also expansion ofthe parts packaging space on the board and reduction in the number ofpackaged parts can be achieved.

Also, according to the present embodiment, in the radio communicationsystem in which the frequency in the transmitting band is lower than thefrequency in the receiving band, the radiation directivity can be easilydirected to the outside of the portable radio device and thus the goodantenna performance can be obtained.

In this case, the similar advantages can be achieved even though theantenna element 12 and the parasitic element 13 are formed of astrip-like metal plate, for example. Also, the method of pasting theantenna element 12 and the parasitic element 13 onto the inner wallsurface of the housing 11 merely shows an example of the antenna holdingmethod. In summary, the similar advantages can be achieved by holdingappropriately the antenna element 12 and the parasitic element 13 intheir adequate positions in the interior of the housing 11. In thisevent, the similar advantages can be achieved even though a monopoleantenna whose effective length corresponds to the half wavelength isused as the antenna element 12.

Second Embodiment

FIG. 5 is a perspective appearance view showing a mobile phone 20corresponding to a particular communication system into which an antennaunit according to a second embodiment of the present invention isincorporated. In this case, in this embodiment, the same referencesymbols are affixed to the same portions as those in the firstembodiment and their duplicate explanation will be avoided herein.

The mobile phone 20 in the present embodiment has the same basicconfiguration as that of the mobile phone 10 shown in FIG. 4 in thefirst embodiment. As the communication system used herein, for example,the receiving frequency of 2300 MHz to 2350 MHz and the transmittingfrequency of 2400 MHz to 2450 MHz are employed respectively and thereceiving frequency is set lower than the transmitting frequencyconversely to the first embodiment.

The mobile phone 20 shown in FIG. 5 has an antenna element 22 and aparasitic element 23 in the rod-like housing 11. A size of the housing11 has a length of 110 mm in the longitudinal direction, a length of 40mm in the width direction, and a length of 15 mm in the thicknessdirection, like the first embodiment.

The antenna element 22 is composed of a half-wave dipole antenna that isfed from the antenna center, and is formed of a copper wire whoseeffective length corresponds to the half wavelength of the receivingfrequency, i.e., whose length is about 65 mm. Here, in the case where noparasitic element 23 is arranged, the frequency band of the mobile phone20 in which the VSWR is 2.5 or less exists in about 2270 to 2360 MHz andalso the bandwidth is almost 90 MHz.

The parasitic element 23 is pasted onto the upper end surface of theinterior of the housing 11 while such parasitic element comes close tothe antenna element 22 at the air clearance d of about 10 mm, and isformed of a copper wire whose effective length corresponds to the halfwavelength of the transmitting frequency, i.e., whose length is about 62mm.

Next, an operation of the antenna unit in the second embodiment will beexplained hereunder. The radiation of the radio wave is executed fromboth the balanced antenna element 22 excited by the feeding portion 14and the parasitic element 23 that is coupled electrically with theantenna element 22. The antenna element 22 mainly operates as theradiator in the transmitting band, while the parasitic element 23operates as the receiver in the receiving band.

In this embodiment, the frequency band of this antenna unit in which theVSWR is 2.5 or less exists in about 2270 to 2360 MHz and about 2390 to2490 MHz, and also a sum of bandwidths becomes about 190 MHz. Thus, theincorporation of the parasitic element 23 yields the wider bandwidth.

Also, the radiation directivity of the present antenna unit results inthe strong radiation in the +X1 direction rather than the −X1 directionsince the parasitic element 23 acts as the waveguide element. Since thereceiving frequency is lower than the transmitting frequency in thiscommunication system, the above radiation directivity can be obtained bypasting the parasitic element 23 whose element length is shorter thanthe antenna element 22 onto the upper end surface of the interior of thehousing 11.

Also, the degradation of the antenna gain is easily brought about by theinfluence of the not-shown board and electronic parts in the housing 11if the radiation to the inward direction of the housing 11 is enhancedconversely to the present embodiment. But the good antenna performancecan be obtained by enhancing the radiation in the outward direction ofthe housing 11 as in this embodiment.

In this manner, according to the present embodiment, the antenna currentis induced in the antenna element 22 at the receiving frequency, whilethe antenna current is induced in the parasitic element 23 at thetransmitting frequency by the spatial coupling between the antennaelement 22 and the parasitic element 23. Therefore, the bandwidth can beexpanded without addition of the matching circuit, and also expansion ofthe parts packaging space on the board and reduction in the number ofpackaged parts can be achieved.

Also, according to the present embodiment, such a radio communicationsystem is constructed that the parasitic element 23 serving as theradiator in the transmitting band is arranged closer to the outside ofthe housing 11 than the antenna element 22 serving mainly as thereceiver in the receiving band and also the frequency in the receivingband is set lower than the frequency in the transmitting band.Therefore, the radiation directivity can be easily directed to theoutward of the portable radio device and thus the good antennaperformance can be obtained.

In the present embodiment, the length of the antenna element 22 must beadjusted within a range of ±10% after the parasitic element 23 isincorporated since the antenna element is also coupled weakly with theparasitic element 23 at the receiving frequency. Similarly, the lengthof the parasitic element 23 must also be adjusted within a range of +10%after the parasitic element is incorporated.

Also, the similar advantages can be achieved even though the strip-likemetal plate is used as the antenna element 22 and the parasitic element23. Also, in the present embodiment, the method of pasting the antennaelement 22 and the parasitic element 23 onto the inner wall of thehousing 11 merely shows an example of the antenna holding method. Insummary, the similar advantages can be achieved by holding appropriatelythe antenna element 22 and the parasitic element 23 in their adequatepositions in the housing 11. In this event, the similar advantages canbe achieved even though a monopole antenna whose effective lengthcorresponds to the half wavelength is used as the antenna element 22.

Third Embodiment

FIG. 6 is an appearance view of a mobile phone 30 of the W-CDMA systeminto which an antenna unit according to a third embodiment isincorporated. In this case, in this embodiment, the same referencesymbols are affixed to the same portions as those in the firstembodiment and their duplicate explanation will be avoided herein.

The mobile phone 30 shown in FIG. 6 has the same basic configuration asthe mobile phone 10 in the first embodiment, and has an antenna element32 and a parasitic element 33 in the rod-like housing 11. Also, in themobile phone 30 in the present embodiment, a length in the longitudinaldirection of the housing 11 is 110 mm, a length in the width directionis 40 mm, and a length in the thickness direction is 15 mm. As with thetransmitting/receiving frequencies in this W-CDMA system, as describedin the first embodiment, the transmitting frequency is 1920 MHz to 1980MHz while the receiving frequency is 2110 MHz to 2170 MHz.

In the antenna unit in the present embodiment, points α, β, γ indicatedby a black dot at three locations in FIG. 6 give a peak point of theantenna current distribution in the transmitting band of this antennaunit respectively. The peak point is scattered into three points. Out ofthree peak points α, β, γ, two points α, β on the antenna element 301have a larger current value than one point y on the parasitic element303. This is because most of the radio waves in the transmitting bandare radiated from this antenna element 32.

The antenna element 32 is composed of a one-wave dipole antenna fed fromthe antenna center, and the effective length corresponds to onewavelength of the transmitting frequency. The antenna element is formedof a copper wire having a length of about 144 mm. In the case where theparasitic element 33 is not arranged, the transmitting frequency band inwhich the VSWR is 2.5 or less exists in about 1910 to 1990 MHz, like thefirst embodiment, and the bandwidth is about 80 MHz.

The parasitic element 33 is pasted onto the upper end surface of theinterior of the housing 11, like the first embodiment, and is formed ofa copper wire whose effective length corresponds to the half wavelengthof the receiving frequency, i.e., whose length is about 70 mm. Also, theparasitic element 33 is arranged in the vicinity of the antenna element32 at the air clearance d of about 10 mm.

Also, in the present embodiment, the length of the antenna element 32must be adjusted within a range of +10% after the parasitic element 33is incorporated. Similarly, the length of the parasitic element 33 mustalso be adjusted within a range of ±10% after the parasitic element isincorporated.

Next, an operation of the antenna unit in the present embodiment will beexplained hereunder.

The transmission/reception of the radio wave are executed by thebalanced antenna element 32 excited by the feeding portion and theparasitic element 33 that is coupled electrically with the antennaelement 32. The antenna element 32 mainly acts as the radiator in thetransmitting band, while the parasitic element 33 acts as the receiverin the receiving band.

Thus, as in the first embodiment, the frequency band of this antennaunit in which the VSWR is 2.5 or less exists in about 1910 to 1990 MHzand about 2100 to 2170 MHz, and also a sum of bandwidths becomes about150 MHz. Thus, the incorporation of the parasitic element 23 gives thewider bandwidth.

Also, the radiation directivity of the present antenna unit results inthe strong radiation in the +X1 direction rather than the −X1 directionsince the parasitic element 33 acts as the waveguide element. Asdescribed above, since the transmitting frequency is lower than thereceiving frequency in the W-CDMA system, the above radiationdirectivity can be obtained by pasting the parasitic element 33 whoseelement length is shorter than the antenna element 32 onto the upper endsurface of the interior of the housing 11.

Also, in this embodiment, the degradation of the antenna gain is easilybrought about by the influence of the board and electronic parts in thehousing 11 if the radiation to the inward direction of the housing 11 isenhanced. But the good antenna performance can be obtained by enhancingthe radiation in the outward direction, like the third embodiment.

Also, the SAR value can be reduced because the peak points in theantenna current distribution are scattered into three points α, β, γ.

In this embodiment, like the first embodiment, the antenna current isinduced in the antenna element 32 at the transmitting frequency, whilethe antenna current is induced in the parasitic element 33 at thereceiving frequency by the spatial coupling between the antenna element32 and the parasitic element 33. Therefore, the bandwidth can beexpanded without addition of the matching circuit, and also expansion ofthe parts packaging space on the board and reduction in the number ofpackaged parts can be achieved.

Also, since the W-CDMA system in which the frequency in the transmittingband is set lower than the frequency in the receiving band is employedas the radio communication system in this embodiment, the radiationdirectivity can be easily directed to the outward of the portable radiodevice and thus the good antenna performance can be obtained. Also, theSAR value can be reduced because of the lower transmitting frequency.Also, the similar advantages can be achieved even though the strip-likemetal plate is used as the antenna element 301 and the parasitic element303.

In this embodiment, the method of pasting the antenna element 32 and theparasitic element 33 onto the inner wall of the housing 11 merely showsone mode of the antenna holding method. The similar advantages can beachieved by holding appropriately the antenna element 32 and theparasitic element 33 in their adequate positions in the interior of thehousing 11.

Fourth Embodiment

FIG. 7 is an appearance view showing a dual-band mobile phone 40 of thecity phone (1.5 GHz PDC) system and the PHS system into which an antennaunit according to a fourth embodiment of the present invention isincorporated. In this case, in this embodiment, the same referencesymbols are affixed to the same portions as those in the firstembodiment and their explanation will be omitted herein.

The mobile phone 40 shown in FIG. 7 has the same basic configuration asthat of the mobile phone 10 shown in FIG. 4 in the first embodiment, andhas an antenna element 42 and a parasitic element 43 in the rod-likehousing 11. Here, the housing 11 of the mobile phone 40 has the samelengths in the longitudinal direction, the width direction, and thethickness direction as the housing 11 in the first embodimentrespectively.

In the antenna unit shown in FIG. 7, peak points in the currentdistribution indicate the peak point of the antenna current upon usingthe city phone system, and are scattered into three points α, β, γ. Inthree points α, β, γ, two points α, β on the antenna element 42 have alarger current value than one point y on the parasitic element 43. Thisis because most of the radio waves upon using the city phone system areradiated from the antenna element 42.

The antenna element 42 is composed of the one-wave dipole antenna fedfrom the antenna center, and the effective length corresponds to onewavelength of the frequency in the city phone system. The antennaelement is formed of a copper wire having a length of about 206 mm.Where the transmitting/receiving frequencies in the city phone systemare 1429 MHz to 1501 MHz (the transmitting band 1429 to 1453 MHz, thereceiving band 1477 to 1501 MHz), and the frequency band in the PHS is30 MHz around 1900 MHz. In the case where the parasitic element 43 isnot arranged, the frequency band in which the VSWR is 2.5 or less existsin about 1425 to 1505 MHz, and the bandwidth is about 80 MHz.

The parasitic element 43 is arranged in the proximity of the antennaelement 42 at the air clearance d of about 10 mm, and pasted onto theupper end surface of the interior of the housing 11. The parasiticelement 43 in this embodiment is formed of a copper wire whose effectivelength corresponds to the half wavelength of the receiving frequency,i.e., whose length is about 79 mm.

Also, in the present embodiment, the length of the antenna element 42must be adjusted within a range of ±10% after the parasitic element 43is incorporated since such antenna element is also coupled weakly withthe parasitic element 43 at the frequency corresponding to the cityphone. Similarly, the length of the parasitic element 43 must also beadjusted within a range of ±10% after the parasitic element 43 isincorporated. Next, an operation of the antenna unit in the fourthembodiment will be explained hereunder.

The transmission/reception of the radio wave are executed by thebalanced antenna element 42 excited by the feeding portion 41 and theparasitic element 43 that is coupled electrically with the antennaelement 42. That is, the antenna element 42 mainly operates as theradiator/receiver in the city phone system, while the parasitic element43 operates as the radiator/receiver in the PHS system.

Thus, the frequency band of this antenna unit in which the VSWR is 2.5or less exists in about 1425 to 1505 MHz and about 1870 to 1930 MHz, andalso a sum of bandwidths becomes about 140 MHz. Therefore, theincorporation of the parasitic element 43 yields the wider bandwidth.

Also, the radiation directivity of the present antenna unit results inthe strong radiation in the +X1 direction rather than the −X1 directionsince the parasitic element 43 acts as the waveguide element. Also, thedegradation of the antenna gain is easily brought about by the influenceof the board and electronic parts in the housing 11 if the radiation tothe inward direction of the housing 11 is enhanced on the contrary tothis embodiment. However, in this embodiment, the good antennaperformance can also be obtained by enhancing the radiation in theoutward direction.

Also, the SAR value can be reduced because the peak points are scatteredinto three points α, β, γ during when the mobile phone 40 is used in thecity phone system. In contrast, in the PHS system, the antenna currentconcentrates at the peak point y on the parasitic element 43, but theSAR value can be disregarded because the maximum transmitting power issmall like 80 mW.

In this embodiment, according to the present embodiment, the antennacurrent is induced in the antenna element 42 in the city phone system,while the antenna current is induced in the parasitic element 43 in thePHS system by the spatial coupling between the antenna element 42 andthe parasitic element 43. Therefore, this antenna unit can meet the dualband without addition of the matching circuit, and also expansion of theparts packaging space on the board and reduction in the number ofpackaged parts can be achieved. Also, the peak points of the current canbe scattered and the SAR value can be reduced.

Also, in this embodiment, the strip-like metal plate may be used as theantenna element 42 and the parasitic element 43. Also, the similaradvantages can be achieved by holding appropriately the antenna element401 and the parasitic element 403 in the interior of the housing 11.Also, the antenna element 42 may be composed of the monopole antennawhose effective length corresponds to the half wavelength.

Fifth Embodiment

FIG. 8 is an appearance view of a mobile phone 50 into which an antennaunit according to a fifth embodiment of the present invention isincorporated. FIG. 9 is a sectional view of the mobile phone 50 takenalong a IX-IX line in FIG. 8. In this case, in this fifth embodiment,the same reference symbols are affixed to the same portions as those inthe third embodiment shown in FIG. 6 and their explanation will beomitted herein.

In the mobile phone 50 shown in FIG. 8 and FIG. 9, unlike the mobilephone 30 in the third embodiment, an earpiece portion 52 as well as theantenna element 32 and the parasitic element 33 is built in the rod-likehousing 11. In this embodiment, the housing 11 has the same lengths inthe longitudinal direction, the width direction, and the thicknessdirection as the housing in the third embodiment respectively. Here, asound source of the earpiece portion 52 is indicated by a listeningpoint 52A in FIG. 9.

The antenna element 32 is pasted and arranged on the inner wall surfaceof the housing 11, which is separated from the listening point 52A by anair clearance L1. The parasitic element 33 is pasted and arranged on theinner wall surface of the housing 11, which is separated from thelistening point 52A by an air clearance L2. Here, the air clearance L1between the listening point 52A and the antenna element 32 is set largerthan the air clearance L2 between the listening point 52A and theparasitic element 33, i.e.,L1>L2  (2)

The earpiece portion 52 is a speaker that converts the electric signalinto the sound, and uses the listening point 52A as the sound source.The listening point 52A is constructed by boring holes through thehousing 11 to pass the sound easily. Normally, the user's ear makescontact with this listening point in the speaking state.

Next, an operation of the antenna unit according to this embodiment willbe explained hereunder.

The transmission/reception of the radio wave are executed by thebalanced antenna element 32 excited by the feeding portion 52 and theparasitic element 33 that is coupled electrically with the antennaelement 32. The antenna element 32 mainly acts as the radiator in thetransmitting band, while the parasitic element 33 acts as the receiverin the receiving band.

(I) Therefore, in the situation that the user puts the listening point52A to the user's ear at the time of transmitting the radio wave, theSAR value can be reduced since the distance L1 between the user's ear(listening point 52A) and the antenna element 32 (the peak points α, β),at which the antenna current is generated strongly in the transmittingstate, can be set larger than the distance L2, as indicated byInequality (2).

In this manner, since the antenna current is induced mainly in theantenna element 32 at the time of transmission, the air clearance L1between the user's ear (listening point 52A) and the peak points α, β ofthe antenna current can be extended and thus the SAR value can bereduced.

(II) In contrast, the antenna current is induced mainly in the parasiticelement at the time of reception, and the air clearance L2 between theuser's ear and the peak point γ of the antenna current becomes smallrather than the air clearance at the time of transmission. But there isno problem because the SAR value is required only of the transmittingoperation.

Also, in this embodiment, the similar advantages can be achieved eventhough the strip-like metal plate is used as the antenna element 32 andthe parasitic element 33. Also, the similar advantages can be achievedby holding appropriately the antenna element 32 and the parasiticelement 33 in the interior of the housing 11. Also, the similaradvantages can be achieved even though the antenna element 32 iscomposed of the monopole antenna whose effective length corresponds tothe half wavelength.

Sixth Embodiment

FIG. 10 is an appearance view of a mobile phone 60 into which an antennaunit according to a sixth embodiment of the present invention isincorporated. FIG. 11 is a sectional view of the mobile phone 60 takenalong a XI-XI line in FIG. 10. In this case, in this embodiment, thesame reference symbols are affixed to the same portions as those in thesecond embodiment shown in FIG. 5 and their explanation will be omittedherein.

In the mobile phone 60 shown in FIG. 10 and FIG. 11 in the sixthembodiment, the antenna element 22 and the parasitic element 23 areprovided to the inside of the rod-like housing 11 and also an earpieceportion 62 is built in the housing 11. In this case, the housing 11 hasthe same lengths in the longitudinal direction, the width direction, andthe thickness direction as the housing in the second embodimentrespectively.

Also, as the communication system applied herein, like the secondembodiment, for example, the receiving frequency of 2300 MHz to 2350 MHzand the transmitting frequency of 2400 MHz to 2450 MHz are employedrespectively and thus the receiving frequency is set lower than thetransmitting frequency.

The antenna element 22 is pasted and arranged on the inner wall surfaceof the housing 11, which is separated from the listening point 62A bythe air clearance L1. The parasitic element 23 is pasted and arranged onthe inner wall surface of the housing 11, which is separated from thelistening point 62A by the air clearance L2.

The earpiece portion 62 is a speaker that converts the electric signalinto the sound, and uses the listening point 62A as the sound source,like the earpiece portion 52 in the fifth embodiment. The listeningpoint 62A is also constructed by boring holes through the housing 11 topass the sound easily. Normally, the user's ear makes contact with thislistening point in the speaking state.

Also, in contrast to the fifth embodiment, the air clearance L1 betweenthe listening point 62A and the antenna element 22 is set smaller thanthe air clearance L2 between the listening point 62A and the parasiticelement 23, i.e.,L1<L2  (3)

Next, an operation of the antenna unit according to this embodiment willbe explained hereunder. In this embodiment, the transmission/receptionof the radio wave are executed by the balanced antenna element 22excited by the feeding portion 14 and the parasitic element 23 that iscoupled electrically with the antenna element 22.

Also, the antenna element 22 mainly operates as the receiver in thereceiving band, while the parasitic element 203 operates as the radiatorin the transmitting band. Therefore, in the situation that the user putsthe listening point 62A to the user's ear upon transmitting the radiowave, the SAR value can be reduced since the distance L2 between theuser's ear (listening point 62A) and the parasitic element 23, in whichthe antenna current acts strongly in the transmitting state, can be setlarger than the distance L1, as indicated by Inequality (3).

In this manner, since the antenna current is induced mainly in theantenna element 32 at the time of transmission, the air clearance L2between the user's ear and the peak points of the antenna current can beextended and thus the SAR value can be reduced.

In contrast, the antenna current is induced mainly in the parasiticelement at the time of reception, and the air clearance L1 between theuser's ear and the peak point of the antenna current becomes smallrather than the air clearance at the time of transmission. But noproblem arises because the SAR value is required only of thetransmitting operation.

Also, like other embodiments, the strip-like metal plate may be used asthe antenna element 22 and the parasitic element 23. Also, the antennaelement 32 and the parasitic element 33 may be held in appropriatepositions in the interior of the housing 11 if the similar advantagescan be achieved. Also, the similar advantages can be achieved eventhough the antenna element 22 is composed of the monopole antenna whoseeffective length corresponds to a half wavelength.

Seventh Embodiment

Next, a seventh embodiment will be explained with reference to FIGS.12(A) to (C) hereunder.

FIG. 12(A) is a perspective view of a printed board 72 constituting apertinent portion of an antenna unit according to the seventh embodimentof the present invention, (B) is an appearance view of a mobile phone 70into which the printed board 72 is incorporated, and (C) is a sectionalview of the mobile phone 70 taken along a XII-XII line in FIG. 12(B). Inthis case, in this embodiment, the same reference symbols are affixed tothe same portions as those in the third embodiment and their explanationwill be omitted herein.

This mobile phone 70 has the same basic configuration as the mobilephone 30 shown in FIG. 6 in the third embodiment. As shown in FIG.12(C), a main board 71, the printed board 72, etc. are provided in theinside of the housing 11.

The antenna element 32 and the parasitic element 33 are constructed onthis printed board 72 as printed patterns. As shown in FIG. 12(C), theprinted board 72 is secured to the inner wall surface of the housing 11of the mobile phone 70.

Here, as the particular fixing method of this printed board 72, forexample, the method of adhering this printed board by using the adhesiveand the double-faced tape, the method of providing ribs on the innerwall surface of the housing 11 and then fitting the printed board 72between the ribs, etc. may be employed.

The antenna element 32 is constructed to receive a signal set from aradio portion 73 on the main board 71 via a feeding pin 74. The feedingpin 74 is formed of a conductive metal, for example, to a top endportion of which a spring structure is provided.

According to such structure, since the antenna element 32 and theparasitic element 33, which are prepared as individual parts in theprior art, can be constructed by the printed patterns formed on a sheetof printed board 72, the number of articles can be reduced. Also, theair clearance between the antenna element 32 and the parasitic element33 can be formed and fixed with high precision, and at the same timethis structure is excellent in mass-producibility. Also, the similaradvantages can be achieved even though the antenna element 32 iscomposed of the monopole antenna whose effective length corresponds toone wavelength.

Eighth Embodiment

Next, an eighth embodiment will be explained with reference to FIGS.13(A) to (C) hereunder.

In FIG. 13, (A) is a perspective view of a printed board 82 constitutinga pertinent portion of an antenna unit according to an eighth embodimentof the present invention, (B) is an appearance view showing a mobilephone 80 into which the printed board 82 is incorporated, and (C) is asectional view of the mobile phone 80 taken along a XIII-XIII line inFIG. 13(B). In this case, in this embodiment, the same reference symbolsare affixed to the same portions as those in the third embodiment shownin FIG. 6 and their explanation will be omitted herein.

This mobile phone 80 has the same basic configuration as the mobilephone 30, and the printed board 82, a main board 83, etc. are providedin the inside of the housing 11.

In the printed board 82 shown in FIG. 13(A), the antenna element 32 andthe parasitic element 33 are constructed on this printed board 82 as theprinted patterns.

Also, a packaged parts 84 and a connector connection terminal 85 areprovided onto the printed board 82. As shown in FIGS. 13(B) and (C), theprinted board 82 is secured to the inner wall surface of the housing 11of the mobile phone 80. Here, as the particular fixing method of thisprinted board 82, for example, the method of adhering this printed boardby using the adhesive and the double-faced tape, the method of providingribs on the inner wall surface of the housing 11 and then fitting theprinted board 82 between the ribs, etc. may be employed.

As the packaged parts 84, for example, an antenna matching circuit, abalance-to-unbalanced transducer (balun), and the like are listed, andpackaged on the printed board 82. Also, the connector connectionterminal 85 is connected to a radio portion 87 on the main board 83 viaa coaxial cable 86.

According to such structure, the packaged parts 84 that are packagedoriginally on the main board 83 can be packaged on the printed board 82as another board, and correspondingly a packaging space on the mainboard 83 can be expanded. In this case, the similar advantages can beachieved even if the power is fed by using the feeding pin 74 set forthin the seventh embodiment in place of the connector connection terminal85 and the coaxial cable 86. Also, in this embodiment, the similaradvantages can be achieved even though the antenna element 32 iscomposed of the monopole antenna whose effective length corresponds toone wavelength.

With the above, the mobile phone 80 using the rod-like housing 11 isexplained in the eighth embodiment. However, the present embodiment canbe applied similarly to a foldable mobile phone 90 shown in FIG. 14, forexample. In this case, in FIG. 14, a reference numeral 91 denotes aliquid crystal display portion (LCD).

More particularly, in the foldable mobile phone 90 shown in FIG. 14, aprinted board 92, which corresponds to the printed board 82 in theembodiment shown in the same figure, and a radio portion 93 may bepackaged on an upper housing 11A and a lower housing 11B respectively.In this event, in this foldable mobile phone 90, the printed board 92and the radio portion 93 can be connected directly via a coaxial cable94.

In the prior art, in the case of such configuration, the power is fed tothe antenna unit by connecting the radio portion in the lower housingand the main board in the upper housing via the coaxial cable andconnecting electrically the main board and the antenna element by usingthe feeding pin, or the like. As a consequence, in the foldable mobilephone in the prior art, the parts such as the feeding ping, etc. areneeded. In contrast, in the foldable mobile phone having the structureaccording to the present invention shown in FIG. 14, the feeding ping,etc. can be omitted and thus the number of articles can be reduced.

Ninth Embodiment

Next, a ninth embodiment will be explained with reference to FIG. 15hereunder.

FIG. 15 is a partially-broken perspective view of a mobile phone 100into which an antenna unit according to a ninth embodiment of thepresent invention is incorporated. In this case, in this embodiment, thesame reference symbols are affixed to the same portions as those in thethird embodiment shown in FIG. 6 and their explanation will be omittedherein.

The mobile phone 100 has the same basic configuration as the mobilephone 30 in the third embodiment, and has a printed board 102 in theinterior of the housing 11. Also, a not-shown radio portion, a feedingportion 104, and the antenna element 32 and the parasitic element 33,both being formed of the printed pattern, are packaged on this printedboard 102. The radio portion is connected electrically to the antennaelement 32 via the feeding portion 104 and is constructed totransmit/receive the signal.

When using such structure, the number of articles can be reduced becausethere is no necessity to construct the antenna element 32 and theparasitic element 33 as the individual parts. Also, the air clearancebetween the antenna element 32 and the parasitic element 33 can beformed and fixed with high precision, and also this structure isexcellent in the mass-producibility. Also, the similar advantages can beachieved even though the antenna element 32 is composed of the monopoleantenna whose effective length corresponds to one wavelength.

Tenth Embodiment

Next, a tenth embodiment will be explained with reference to FIG. 16hereunder.

FIG. 16 is an appearance view of a mobile phone 110 into which anantenna unit according to a tenth embodiment of the present invention isincorporated. In this case, in this embodiment, the same referencesymbols are affixed to the same portions as those in the thirdembodiment and their explanation will be omitted herein.

The mobile phone 110 according to this tenth embodiment has also thesame basic configuration as the mobile phone 30 shown in FIG. 6 in thethird embodiment, and has the meander antenna element 32 and the meanderparasitic element 33 in the rod-like housing 11. In this manner, sincethe antenna element 32 and the parasitic element 33 are shaped like themeander shape, both electrical lengths of the antenna element 32 and theparasitic element 33 can be tuned to a desired frequency band relativelyfreely. In addition, these elements can be formed together compactly toreduce the size.

Therefore, according to this configuration, these elements can beconstructed small in size by forming the antenna element 32 and theparasitic element 33 like the meander. In this case, only any one of theantenna element 32 and the parasitic element 33 may be formed in themeander fashion to reduce the size. Also, the similar advantages can beachieved even though the antenna element 32 and the parasitic element 33are formed helically.

Eleventh Embodiment

Next, an eleventh embodiment will be explained with reference to FIG. 17hereunder.

FIG. 17 is a schematic perspective view of a mobile phone 120 into whichan antenna unit according to an eleventh embodiment of the presentinvention is incorporated. In this case, in this embodiment, the samereference symbols are affixed to the same portions as those of themobile phone 30 shown in FIG. 6 in the third embodiment and theirexplanation will be omitted herein. This mobile phone 120 has also thesame basic configuration as the mobile phone 30 in the third embodiment.The mobile phone 120 has the antenna element 32 being fed balancedly inthe interior of the rod-like housing 11. This antenna element 32 iscomposed of the dipole antenna like the third embodiment.

Such balanced feeding of the antenna element 32 makes it difficult forthe antenna current to flow through the housing 11 of the mobile phone120. As a result, the antenna that is seldom affected by the user's handwhen the user holds the phone in use can be realized, and thus theexcellent antenna characteristics can be kept/realized in the actualservice condition.

As described above, according to the present invention, because theantenna unit having the antenna element and the parasitic element isbuilt in the portable radio device, the wider bandwidth can be realizedand also the good antenna performance can be realized by controlling theradiation directivity. In addition, according to this invention, becausethe antenna is never exposed to the outside of the housing, the antennaunit and the portable radio device, which are in no way damaged by thecontact, have a high reliability, and are convenient to use, can beimplemented.

In addition, according to the present invention, because the SAR valuecan be reduced by scattering the peak point of the antenna current intoplural points, the antenna unit and the portable radio device, which areexcellent in respect of safety, can also be realized.

The present invention is explained in detail with reference toparticular embodiments. But it is apparent for the person skilled in theart that various variations and modifications may be applied withoutdeparting a spirit and a scope of the present invention.

This application is filed based on Japanese Patent ApplicationNo.2002-38546 filed on Feb. 15, 2002 and the contents thereof areincorporated by the reference herein.

INDUSTRIAL APPLICABILITY

According to the present invention, since the antenna unit having theantenna element and the parasitic element is built in the portable radiodevice, the wider bandwidth can be realized and also the good antennaperformance can be realized by controlling the radiation directivity.

Also, according to this invention, since the antenna is never exposed tothe outside of the housing by incorporating the antenna element and theparasitic element into the interior of the housing of the portable radiodevice, the antenna unit and the portable radio device, which are by nomeans damaged by the contact, have a high reliability, and areconvenient to use, can be realized.

1. An antenna unit used in a portable radio device comprising: anantenna element; and a parasitic element, wherein the antenna elementhas an effective length corresponding to a half wavelength or onewavelength of a transmitting frequency, to induce an antenna currentthat radiates the transmitting frequency upon transmitting a radio wavein a predetermined transmitting frequency band, and wherein theparasitic element has an effective length corresponding to a halfwavelength of a receiving frequency, to induce another antenna currentby a spatial coupling with the antenna element upon receiving the radiowave in a predetermined receiving frequency band.
 2. An antenna unitused in a portable radio device comprising: an antenna element; and aparasitic element, wherein the antenna element has an effective lengthcorresponding to a half wavelength of a receiving frequency, to inducean antenna current upon receiving a radio wave in a predeterminedreceiving frequency band, and wherein the parasitic element has aneffective length corresponding to a half wavelength of a transmittingfrequency, to induce another antenna current by a spatial coupling withthe antenna element upon transmitting the radio wave in a predeterminedtransmitting frequency band.
 3. An antenna unit used in a portable radiodevice that executes transmission/reception based on a communicationsystem using radio waves in a plurality of different wavelength bands,said antenna unit comprising: an antenna element; and a parasiticelement, wherein the antenna element has an effective lengthcorresponding to a half wavelength or one wavelength of a frequency inone communication system, to induce an antenna current upon using onecommunication system, and wherein the parasitic element has an effectivelength corresponding to a half wavelength of a frequency in othercommunication system, to induce another antenna current in the parasiticelement by a spatial coupling with the antenna element upon using theother communication system.
 4. The antenna unit according to any one ofclaims 1 to 3, wherein the portable radio device comprises an earpieceportion, and wherein a distance between the earpiece portion and theantenna element is set larger than a distance between the earpieceportion and the parasitic element.
 5. The antenna unit according to anyone of claims 1 to 4, wherein the portable radio device comprises anearpiece portion, and wherein a distance between the earpiece portionand the antenna element is set shorter than a distance between theearpiece portion and the parasitic element.
 6. The antenna unitaccording to any one of claims 1 to 5, wherein the antenna element andthe parasitic element are formed by printed patterns on a sheet ofprinted board.
 7. The antenna unit according to claim 6, whereinelectronic parts are packaged on the printed board.
 8. The antenna unitaccording to any one of claims 1 to 7, wherein the portable radio devicefurther comprises a radio portion and a printed board on which the radioportion is mounted, and wherein the antenna element and the parasiticelement are formed by printed patterns on the printed board.
 9. Theantenna unit according to any one of claims 1 to 8, wherein any one orboth of the antenna element and the parasitic element is or are shapedlike a meander shape.
 10. The antenna unit according to any one ofclaims 1 to 9, wherein the antenna element is balancedly fed.
 11. Theantenna unit according to any one of claims 1 to 10, wherein the antennaelement and the parasitic element are arranged in an interior of ahousing of the portable radio device.
 12. A portable radio device havingthe antenna unit set forth in any one of claims 1 to 11.